U.S. patent application number 14/465777 was filed with the patent office on 2015-02-26 for fully wireless continuously wearable sensor for measurement of eye fluid.
The applicant listed for this patent is CALIFORNIA INSTITUTE OF TECHNOLOGY. Invention is credited to Muhammad MUJEEB-U-RAHMAN, Axel SCHERER.
Application Number | 20150057516 14/465777 |
Document ID | / |
Family ID | 52480963 |
Filed Date | 2015-02-26 |
United States Patent
Application |
20150057516 |
Kind Code |
A1 |
MUJEEB-U-RAHMAN; Muhammad ;
et al. |
February 26, 2015 |
FULLY WIRELESS CONTINUOUSLY WEARABLE SENSOR FOR MEASUREMENT OF EYE
FLUID
Abstract
Novel methods and systems for monitoring the health of an eye
are disclosed. For example, a resonant circuit may be fabricated on
a contact lens and this circuit may be coupled to a second circuit
having the same resonant current frequency. A change in a property
of the eye fluid contacted by the sensor in the contact lens is
communicated to an external device and a remedying action is
suggested to the wearer.
Inventors: |
MUJEEB-U-RAHMAN; Muhammad;
(PASADENA, CA) ; SCHERER; Axel; (BARNARD,
VT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CALIFORNIA INSTITUTE OF TECHNOLOGY |
PASADENA |
CA |
US |
|
|
Family ID: |
52480963 |
Appl. No.: |
14/465777 |
Filed: |
August 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61869540 |
Aug 23, 2013 |
|
|
|
Current U.S.
Class: |
600/346 ;
427/2.12; 600/345; 600/348 |
Current CPC
Class: |
H05K 3/146 20130101;
A61B 3/101 20130101; A61B 5/0531 20130101; H05K 3/1216 20130101;
H05K 3/0014 20130101; A61B 5/14507 20130101; H05K 1/16 20130101;
H05K 2201/0108 20130101; A61B 5/14517 20130101; A61B 2560/0219
20130101; H05K 2201/10151 20130101; A61B 5/6821 20130101; A61B
5/0031 20130101; A61B 5/0538 20130101 |
Class at
Publication: |
600/346 ;
600/345; 600/348; 427/2.12 |
International
Class: |
A61B 3/10 20060101
A61B003/10; A61B 5/00 20060101 A61B005/00; H05K 3/00 20060101
H05K003/00; H05K 3/14 20060101 H05K003/14; H05K 3/12 20060101
H05K003/12; A61B 5/145 20060101 A61B005/145; C23C 16/06 20060101
C23C016/06 |
Claims
1. A resonant sensor comprising: a first resonant circuit,
comprising at least one first resistor, at least one first
capacitor and at least one first inductor, wherein the first
resonant circuit is configured so that an eye fluid in contact with
the resonant sensor will electrically connect at least two points
in the first resonant circuit, and a change in at least one
property of the eye fluid will effect a change in a resonant
behavior of the first resonant circuit.
2. The resonant sensor of claim 1, wherein a shape of the at least
one first capacitor, of the at least one first resistor, and/or the
at least one first inductor is configured so as to give a desired
value of a resonant current frequency.
3. The resonant sensor of claim 1, wherein the at least one first
resistor, at least one first capacitor and at least one first
inductor are metal traces on a wearable contact lens.
4. The resonant sensor of claim 3, wherein a shape, length and
overlap of the metal traces is configured so as to give a desired
value for a resonant current frequency of the first resonant
circuit.
5. A system comprising the resonant sensor of claim 1, further
comprising: a second resonant circuit, comprising at least one
second resistor, at least one second capacitor and at least one
second inductor, wherein the at least one second inductor is
configured to be electromagnetically coupled to the at least one
first inductor, and wherein the first and second resonant circuits
have a same resonant current frequency; and a reader configured to
communicate with the second resonant circuit, thereby obtaining a
measurement of the change in the resonant current frequency.
6. A system comprising the resonant sensor of claim 4, further
comprising: a second resonant circuit, comprising at least one
second resistor, at least one second capacitor and at least one
second inductor, wherein the at least one second inductor is
configured to be electromagnetically coupled to the at least one
first inductor, and wherein the first and second resonant circuits
have a same resonant current frequency; and a reader configured to
communicate with the second resonant circuit, thereby obtaining a
measurement of the change in the resonant frequency.
7. The resonant sensor of claim 1, wherein the at least one
property of an eye fluid is its resistance or conductance.
8. The resonant sensor of claim 1, wherein the at least one
property of an eye fluid is a concentration of a biological or
chemical agent.
9. The resonant sensor of claim 8, wherein the biological or
chemical agent is Anthrax.
10. A method to monitor a health state of an eye, the method
comprising: applying the system of claim 6 to the eye; measuring
the at least one property of the eye fluid; detecting the change in
the resonant current frequency; relating the change in the resonant
frequency to the change in the at least one property of the eye
fluid; and communicating the change in the at least one property of
the eye fluid.
11. The method of claim 10, further comprising, based on the
communicating, and suggesting a remedying action to a wearer of the
wearable contact lens.
12. A method to fabricate the resonant sensor of claim 1,
comprising printing a metallic circuit on a flexible biocompatible
substrate.
13. A method to fabricate the resonant sensor of claim 1,
comprising direct metal coating on a flexible polymer by thin film
deposition or thick film deposition.
14. The method of claim 13, wherein the thin film deposition is
physical vapor deposition or chemical vapor deposition.
15. The method of claim 13, wherein the thick film deposition is
screen printing.
16. The resonant sensor of claim 1, wherein the first resonant
circuit is fabricated on a flexible substrate shaped like a contact
lens.
17. The method of claim 12, further comprising shaping the flexible
biocompatible substrate like a contact lens by thermal
processing.
18. The method of claim 17, wherein the thermal processing is hot
embossing or vacuum forming.
19. The resonant sensor of claim 16, further comprising a hole in a
pupil area to increase transparency.
20. A method to measure sweat on a skin with the resonant sensor of
claim 1, comprising configuring the resonant sensor to detect at
least one property of sweat.
21. The method of claim 12, further comprising functionalizing the
resonant sensor with a hydrogel or a polymer containing a desired
chemistry.
22. The method of claim 21, wherein the polymer is an ion-sensitive
membrane.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Patent Application No. 61/869,540, filed on Aug. 23, 2013, the
disclosure of which is incorporated herein by reference in its
entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to biological sensing. More
particularly, it relates to a fully wireless continuously wearable
sensor for measurements of eye fluid.
BRIEF DESCRIPTION OF DRAWINGS
[0003] The accompanying drawings, which are incorporated into and
constitute a part of this specification, illustrate one or more
embodiments of the present disclosure and, together with the
description of example embodiments, serve to explain the principles
and implementations of the disclosure.
[0004] FIG. 1 illustrates an exemplary circuit.
[0005] FIG. 2 illustrates a plot of a resonant frequency and
current amplitude.
[0006] FIG. 3 illustrates primary and secondary circuits connected
through coils.
[0007] FIG. 4 illustrates an exemplary contact lens with metal
traces.
[0008] FIG. 5 illustrates an exemplary contact lens with metal
traces and specific polymers.
[0009] FIG. 6 illustrates differently shaped capacitors.
[0010] FIG. 7 illustrates three dimensional capacitors.
[0011] FIG. 8 illustrates a three dimensional metal trace.
[0012] FIG. 9 illustrates a sensing system.
SUMMARY
[0013] In a first aspect of the disclosure, a resonant sensor is
described, the resonant sensor comprising: a first resonant
circuit, comprising at least one first resistor, at least one first
capacitor and at least one first inductor, wherein the first
resonant circuit is configured so that an eye fluid in contact with
the resonant sensor will electrically connect at least two points
in the first resonant circuit, and a change in at least one
property of the eye fluid will effect a change in a resonant
behavior of the first resonant circuit.
DETAILED DESCRIPTION
[0014] The human eye is a very sensitive organ and its proper
operation depends upon many factors; presence of proper eye fluids
(e.g. tear fluid) is a very important one of these factors.
Decrease in these fluids leads to a condition commonly known as dry
eye. This can lead to discomfort, mild to severe damage to the
ocular surface and to long term inflammation. Measurement of the
eye fluid involves measuring its level as well as its constituents;
both of which affect the proper function of the eye. In the present
application, a fully wireless and wearable eye sensor is described
which can measure the required properties of eye fluids through
electrical measurements. The sensor uses resonantly coupled
devices, where a change in the resonance properties of the wearable
device is induced by a change in the eye fluid. This change in
resonance properties is coupled to an external module which relays
the information to a data display device to transfer the
information to a user or a medical practitioner.
[0015] Measurement of eye fluids can provide a very useful measure
on the health of the eye. However, most of these measurements are
taken at discrete intervals using special instruments, which make
it less useful for a person who is at permanent risk of eye damage
due to dry eye disease or some other eye disease. Measurement of
eye fluids can also be used to measure the concentration of toxins
or pollutants in the environment as they become soluble in the eye
fluids. Development of minimally invasive and continuous sensors
for this purpose can lead to many advantages for such
applications.
[0016] In the present application, the design of sensors is
described utilizing electrical resonators. This type of sensor can
operate in both active and passive modes. The design is very
flexible and can be targeted to detect different chemical species
in the eye fluid.
[0017] As known to the person skilled in the art, a passive
electrical resonator consists of two different energy storing
elements, i.e. an inductor and a capacitor, and an energy
dissipating resistor, due to the finite (non zero) conductivities
of materials used. These electrical elements can be connected in
series or parallel. A series circuit is shown as an example in FIG.
1. In FIG. 1, a resistor (105), a capacitor (115) and an inductor
(110) are visible.
[0018] The current amplitude in the circuit of FIG. 1 depends on
the frequency of the electrical current flowing through the
circuit, due to the frequency dependence of capacitive and
inductive impedances. A typical response can be plotted as in FIG.
2. As known to the person skilled in the art, an alternative
current (AC), that is a current that is not constant, but has a
value varying in time, interacts in a fundamentally different way
with discrete components of an electrical circuit. The reason is
that the capacitance and the inductance, in particular, have a
value that is a function of the frequency of the current. For
example, a current may have a sinusoidal temporal variation.
[0019] In FIG. 2, three exemplary cases are displayed, with a low
resistance R (205), a medium resistance (210) and a high resistance
(215). As known to the person skilled in the art, a low resistance
will give a high resonance peak for the current, while a high
resistance with give a low resonance peak value for the current in
the circuit. Therefore, for example, a change in the value of the
resistance can be detected by its effect on the amplitude of the
resonant current in the circuit. Since this change in value can be
high due to resonant effect, then the circuit is able to detect
small changes in resistance at or close to the resonant
frequency.
[0020] In circuits similar to that of FIG. 2, the frequency for the
maximum (e.g. peak) current amplitude corresponds to a resonance
conditions given by:
fr = 1 2 .pi. LC ( Hz ) ##EQU00001##
[0021] where f.sub.r is the resonant frequency, L is the inductance
and C is the capacitance. The frequency is measured in Hz. The
height and sharpness of the peak at this resonant frequency f.sub.r
is given by another quantity described as the quality factor Q:
Q = 1 R L C ##EQU00002##
[0022] where R is the resistance, L is the inductance and C is the
capacitance.
[0023] According to the equations above, the magnitude of the
resonant frequency depends upon the value of frequency-dependent
parameters, such as capacitive and inductive impedances, C and L
respectively. The quality factor Q (and other quantities such as
the maximum amplitude of the resonant current) depends upon the
energy dissipating element as well, such as the resistance R.
[0024] If an external signal loads the circuit, for example by
providing a resistance path for the current, the external load
changes the resonance behavior based upon the type of loading. A
change in L or C will change the resonant frequency and a change in
R will change the height of the resonant peak and its width.
[0025] In some embodiments, the sensors of the present disclosure
comprise two coils which connect two circuits. The coils can be
termed primary and secondary. The primary and secondary coils can
connect two circuits through their induced electrical effects and
magnetic fluxes. In some embodiments, a first circuit with one coil
can be implanted in a biological tissue or organ, such as the eye.
The other circuit with the second coil may be external to the body.
Through the electromagnetic effects active between the two coils,
the two separate circuits can be coupled.
[0026] For example, the secondary coil may be in a circuit embedded
in the eye, where changes in the eye fluids may affect the
electrical properties of the circuit. Through the secondary coil
coupling to the primary coil, where the primary coil is part of a
circuit external to the body, the measurement related to eye fluids
can be communicated externally to another circuit, and can then be
read by a user or medical practitioner.
[0027] In the present disclosure, the resonator circuits can be
designed to be loaded by the sensing signal in different ways. For
example, two electrodes of the resonator circuit may be open to
direct contact by the eye fluid, while the remaining components of
the circuit are electrically insulated from the eye fluid. The eye
fluid, in this embodiment, will act as a conductive channel between
the two electrodes. The conductivity of the eye fluid depends on
various factors, such as the concentration of chemical and
biological components, and the amount of water. For example, if the
eye is dry, less eye fluid will be present; therefore its
conductivity will decrease. In this case, the resistance between
the two electrodes would increase, thereby changing the resonance
frequency of the resonator circuit. In one embodiment, a change in
the eye fluids conductivity will change the value of the resistance
between two separate coils. The coils can act as inductors.
[0028] In another embodiment, a change in the eye fluid's
conductivity will change the series resistance within one coil.
Therefore, different embodiments may have different numbers of
coils. As known to the person skilled in the art, coils may have
different amounts of windings or turns, which may affect the total
inductance of the coils.
[0029] In yet another embodiment, a change in the capacitance
between the coil turns or between different coils is caused by a
change in the permittivity of the eye fluid. As known to the person
skilled in the art, the permittivity is a property that can affect
the value of electrical quantities. All these changes, as listed in
the different embodiments above, can affect the resonance behavior
of the secondary coil, which affects the primary coil due to
resonant coupling between the two, as known to the person skilled
in the art.
[0030] The change in the resonance of the implanted coil
(`secondary`) affects another coil (`primary`), which is in
resonance with the primary coil. The primary and secondary coils
may have the same resonance frequency. The primary coil is outside
the body. This change is detected as a change in the voltage across
the primary inductor by a voltage reader and is indicative of the
corresponding measurement of eye fluids.
[0031] In FIG. 3, the secondary circuit is illustrated as a
parallel circuit, but in other embodiments series circuits may be
used. In FIG. 3, a secondary circuit (305) is shown, which can be
implanted in the human eye. A primary circuit (310) is external and
is used to retrieve electrical measurements from the secondary
circuit (305). The primary coil (320) couples to the secondary coil
(315). In other words, the primary circuit (310) can be part of an
external device, while the secondary circuit (305) can be part of
the device in the contact lens. The two primary (320) and secondary
(305) circuits can be coupled through their respective coils.
[0032] The overall sensors of the present disclosure can be
designed as a combination of electrical elements in the form of
distributed inductors, capacitors and resistors made with noble
metals on a wearable contact lens. This is a minimally invasive
design and it is user-replaceable. In this embodiment, the sensor
is a contact lens.
[0033] The sensor is on the eye side so that it can access eye
fluids more easily. The substrate can be a biocompatible soft
material which can support the fabrication process as well as the
sensor operation inside the eye. Some example designs are shown in
FIGS. 4-5.
[0034] In FIG. 4, a contact lens (410) is illustrated, where the
pupil is visible schematically (405). Exemplary metal traces (415,
420) are also illustrated. These traces may be optionally covered
with polymer to avoid metal-eye contact. The polymer can be water
permeable to allow eye fluid access the sensor.
[0035] In FIG. 5 another example of a contact lens sensor (505) is
illustrated. Metal traces (510, 515) are visible and optionally
some parts of the metal traces (510, 515), specifically parts (520,
525), may be covered with selective polymers or hydrogels.
[0036] The exposed edges (520, 525) can be coated with different
coatings, which are sensitive to different biological species and
this converts this basic system into a sensor for specific targets.
For example, a coating sensitive to a particular biological entity
may be used, and the sensor will detect the presence or absence of
that particular biological entity.
[0037] The value of the inductance and capacitance in the resonant
circuit can be controlled to make the device resonate at a desired
frequency where electromagnetic absorption through the substrate
and the eye is minimal or where the electromagnetic band is most
suitable in terms of signal quality. External inductors and/or
capacitors can be added to achieve the desired frequency range, if
needed.
[0038] The capacitance can be controlled by controlling the shape
and material of the electrical elements, and by increasing the
cross sectional overlap. One example is to use twisted conductor
lines to increase the cross-sectional area of the capacitor as
shown in FIG. 6. In FIG. 6, a first conductor (605) constitutes one
plate of a capacitor, while a second conductor (610) constitutes a
second plate. Different shapes will give a different capacitance.
Interdigitated structures can also be used to increase
capacitance.
[0039] The capacitance can also be controlled or increased by
increasing the surface area of the capacitor using micromachining
and producing 3D capacitors. This is shown in FIG. 7.
[0040] In FIG. 7, a first conductor (705) is separated from a
second conductor (715) by a dielectric layer (710).
[0041] The inductance can be controlled or increased by using
raised structures as shown in the 3D geometry, for example, of FIG.
8, using micromachining. In FIG. 8, a metal track (805) is shown,
which can be used to form some or all of the electrical components
of a circuit.
[0042] Therefore, as described in the present disclosure, a
wearable contact lens comprises a suitable sensor on it. The sensor
part can face the eye. The sensor will be resonantly coupled to an
external device which can be kept in closed vicinity of the eye(s)
(e.g. on glasses). This external device can then connect (e.g.
remotely) to a smartphone or other computers, for continuous data
storage, showing data trends and displaying proper messages and
signal levels. This system is shown in FIG. 9.
[0043] In the system illustrated in FIG. 9, a contact lens with a
sensor is illustrated (905). The lens (905) is connected (e.g.
coupled) to an external device (910). The external device (910) may
have a resonator coupled to the implanted resonator, through the
primary and secondary coils as described above in the present
disclosure. The device (910) may also comprise a power supply and a
communication device, which allows communication (e.g. remote) with
a computer, tablet or smartphone (915). The smartphone (915) may
have a smart application (App) to display sensor data and actuate
corresponding actions (e.g. displaying a message `put drops in the
left eye`).
[0044] In some embodiments, the sensor has metal traces, which form
a resonator circuit where the role of the resistance (or variation
thereof) is played by the eye fluid. For example, the circuit may
have two open electrodes where the resistor should be and the
electrodes are configured so as to allow the eye fluid to be in
contact with the electrodes. Therefore, the eye fluid, being an
electrically conducting fluid with a resistance, will short the two
electrodes and act as a resistance for the resonator circuit. The
conductivity of the eye fluid will change depending, for example,
on the amount of eye fluid. Therefore, in some embodiments, a dry
eye will have a different resistance than a lubricated eye. In such
cases, the resonant circuit will detect the change in resistance
through the change in the resonant frequency.
[0045] In some embodiments, chemical or biological agents present
in the atmosphere can be detected by eye sensors such as the
sensors described in the present disclosure, which are embedded in
a contact lens. When an agent is present in the air, for example
Anthrax, the agent will most likely interact with the surface of
the eyes as it is normally exposed and more permeable than skin. In
this way, a sensor can detect the presence of such agent by
integrating a corresponding chemical sensor in the contact
lens.
[0046] In some embodiments, the resistor of a circuit may be the
parasitic resistance of the inductance and/or the capacitance in
the circuit, instead of a discrete resistor. Alternatively, the
resistor may be the eye fluid connected between two electrodes of
the circuit, as described above in the present disclosure. In some
embodiments, all these different types of resistance may be
coexistent and indicated overall with the term `resistor`.
[0047] Different methods may be used to fabricate the devices of
the present disclosure.
[0048] A suitable metal (e.g. gold) plated printed circuit board
(PCB) on flexible biocompatible substrate (e.g. polyimide) may be
used. Direct metal coating on flexible polymers (e.g. PET) using
thin film deposition methods (e.g. physical vapour deposition PVD,
or chemical vapour deposition CVD) or thick film methods (e.g.
screen printing) may be used.
[0049] The flexible substrates can have the shape of a contact lens
to begin with or can be shaped after fabrication using thermal
processing (e.g. hot embossing or vacuum forming).
[0050] A hole can be made in the contact lens in the pupil area if
more transparency is needed. This can be useful for PCB based
systems.
[0051] The sensors can be used on the skin as well for simple
analysis of level of sweating or conductivity of sweat itself.
Multiple such sensors can be used to determine the required
information.
[0052] Functionalization can be done by dip-coating the sensitive
area (the exposed area) of the sensor with a hydrogel or a polymer
containing the desired chemistry (e.g. ion-sensitive membranes).
The mixtures can also be pipetted on the desired area and let to
gel or dry in-situ.
[0053] In some embodiments, the sensors can be fabricated on
contact lenses (or any material already shaped for final
application) using stencils (e.g. stick-n-peel type).
[0054] Aligned lithography can be done for multi-step fabrication
(e.g. passivating parts of metal lines).
[0055] A number of embodiments of the disclosure have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the present disclosure. Accordingly, other embodiments are
within the scope of the following claims.
[0056] The examples set forth above are provided to those of
ordinary skill in the art as a complete disclosure and description
of how to make and use the embodiments of the disclosure, and are
not intended to limit the scope of what the inventor/inventors
regard as their disclosure.
[0057] Modifications of the above-described modes for carrying out
the methods and systems herein disclosed that are obvious to
persons of skill in the art are intended to be within the scope of
the following claims. All patents and publications mentioned in the
specification are indicative of the levels of skill of those
skilled in the art to which the disclosure pertains. All references
cited in this disclosure are incorporated by reference to the same
extent as if each reference had been incorporated by reference in
its entirety individually.
[0058] It is to be understood that the disclosure is not limited to
particular methods or systems, which can, of course, vary. It is
also to be understood that the terminology used herein is for the
purpose of describing particular embodiments only, and is not
intended to be limiting. As used in this specification and the
appended claims, the singular forms "a," "an," and "the" include
plural referents unless the content clearly dictates otherwise. The
term "plurality" includes two or more referents unless the content
clearly dictates otherwise. Unless defined otherwise, all technical
and scientific terms used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which the
disclosure pertains.
* * * * *